In the technology development for fabricating a semiconductor package, leads used as I/O connections are increasingly disposed in number and density in the semiconductor package. Further, due to enhancement in integrated circuit performance for a semiconductor chip, heat generated by the chip is accordingly increased. Therefore, it is critical for the heat to be effectively dissipated to the atmosphere, so as to assure the quality of the chip and semiconductor package.
In order to solve the heat dissipating problem for the semiconductor package, conventionally a heat sink or heat block made of conductive metal such as copper or aluminum is applied to the semiconductor package, or alternatively, cooled air or liquid is passed through a surface of the semiconductor package, so as to allow the heat generated by the chip to be effectively and rapidly dissipated to the atmosphere. Moreover, shortening a heat dissipating path is advantageous for improving heat dissipating efficiency. That is, if the semiconductor package is constructed in a manner that, the heat spreader or heat block comes into direct contact with the chip and has a surface thereof exposed to outside of an encapsulant in the semiconductor package, the shortest heat dissipating path can be achieved, and thus the heat dissipating efficiency can be effectively improved.
U.S. Pat. No. 5,851,337 provides a semiconductor package with an exposed heat sink. As shown in FIG. 1, this semiconductor package comprises a substrate 1; a semiconductor chip 2 mounted on the substrate 1; a plurality of cove elements 3 such as gold wires for electrically connecting the substrate 1 to the chip 2; and an exposed heat sink 4 attached to the substrate 1 and the chip 2 respectively by means of an adhesive 6; an encapsulant 5 for encapsulating the substrate 1, the chip 2, the conductive elements 3 and the heat sink 4; and a plurality of solder balls 7 implanted on an exposed surface of the substrate 1. As the heat sink 4 is in direct contact with the chip 2, heat generated by the chip 2 can be easily dissipated through an exposed sure of the heat sink 4 to the atmosphere or to a heat dissipating device (not shown), such as a heat pipe or fan, externally attached to the exposed surface of the heat ink 4. This therefore makes the semiconductor package significantly improved in heat dissipating efficiency.
However, in a molding process for the semiconductor package disclosed in the foregoing U.S. Pat. No. 5,851,337, as shown in FIG. 2, it occurs that the heat sink 4 is pressed by an upper mold 8a and a lower mold 8b during engaging the molds, due to the heat sink 4 having a height greater than a depth of a molding cavity. This then makes the chip 2 pressed by the heat sink 4, and eventually results in damage or cracks 9 on the chip 2. In this case, the package quality and fabrication cost are undesirably affected. The reason for the heat sink 4 excessive in height is that the adhesive 6 used for attaching the heat sink 4 to both the substrate 1 and the chip 2 is hardly controlled in thickness. That is, if the adhesive 6 is made too thick, then the height of the heat sink 4 will exceed the depth of the molding cavity. Besides, dimensional inaccuracy in manufacture for the heat sink 4 can also lead to the heat sink 4 higher in elevation than the depth of the molding cavity.